1. Field of the Invention
The present invention relates to an image forming apparatus which uses fuzzy inference, such as an electronic photography copier, and an electronic photography laser printer, which uses electrostatic images.
2. Related Background Art
It is well known that to obtain a high-quality image, desired potential must be supplied to a light-sensitive body (an image bearing member) in a charging process and a development bias must be set appropriately in a development process. Since a desired potential and a development bias differ depending upon room temperature, humidity, original density, the accumulated number of copied sheets or the like, these conditions must be considered at all times when the set values of a potential and a development bias are determined. Several examples about the relation between these conditions (state quantities), and a potential and a development bias (control quantities) will be described next.
When humidity is high, the surface of a light-sensitive body and a supporting member supporting it are moistened and a surface resistance value decreases. As a result, when electric charges are supplied to a light-sensitive body by a charging apparatus, some of the charges escape from the light-sensitive body and a desired potential cannot be obtained. For this reason, output from a charging apparatus must be increased under a high humiditY environment.
The fact that the density of a copy image varies with the density of the original is known. When high-density originals are copied in succession, the density of a copy image becomes high and a development agent is deposited on a white ground section, or, when low-density originals are copied in succession, the density of a copy image becomes low. Therefore, when the density of an original is high, a dark potential (potential after charging) must be set low or a development bias must be set high. When the density of an original is low, a dark potential must be set high, or a development bias must be set low.
In addition, when the number of copies is increased, the electrical capacity of a light-sensitive body increases as a result of the thickness of the light-sensitive layer becoming thinner and a required dark potential cannot be obtained. This results from the fact that the surface of a light-sensitive body is scratched, since after a visual image is transferred onto a transfer material (image bearing member), it passes through a process in which a remaining development agent on the light-sensitive body is scraped off with a brush or an elastic member (process of cleaning a light-sensitive body). Taking this factor into account, the output from a charging apparatus must be increased as the number of copies is increased.
As for the relation between various kinds of state quantities and control quantities mentioned above, the variations in all the state quantities cannot be corrected by using a single set value under the present situation. Hence, the output level in response to work is switched or output linked with a sensor is automatically set. Or, in some cases, no action is taken.
The switching of an output value in response to work entails much labor and the difficulty of judging switching timing. In particular, when judging switching timing, an appropriate output value must be found in which a number of conditions are considered simultaneously and decision criterion is entrusted to past experience based on much experimental data. A person who is not well informed about these criteria will have difficulty in judging switching timing. Also, if it is desired to set the output level to a more desired value, a plurality of output levels need to be held in memory and therefore the apparatus becomes expensive.
In addition, to set output automatically, a complex output control program must be prepared on the basis of a low of experimental data. As mentioned above, it is necessary to find an appropriate output value experimentally for a case where each of the conditions varies. A vast experimental data table is required before a program can be written and a lot of time and labor are needed. Actually, in many cases, many conditions cannot be taken into account and only those conditions which are particularly important are considered. In order to meet the need in recent years to improve the reliability of this kind of image forming apparatus, output control automation rather than the output value switching method, and a method of preparing a simple control program capable of easily taking in many conditions have been desired.
In a image forming apparatus, for example, a post charger (for supplying a uniform corona to a light-sensitive body before transferring to increase transfer efficiency), a transfer charging apparatus, and separation charger of an electronic photography copier include an apparatus that supplies charges to a toner image on a light-sensitive body from the outside, transfers the toner image onto a transfer material, and separates the transfer material from the light-sensitive body.
In particular, in a high-speed apparatus with a process speed exceeding about 400 mm/sec, regarding the charging quantity of each charger, factors such as the characteristics of a toner on a light-sensitive body, i.e., the quantity of charges of a toner (dependent on the state of an original), kinds of transfer materials, the state under which a transfer material is moistened, the transfer speed of a main body, the history state, such as the dirtiness of each charger, and so on are considered, and the set value of each charger output is obtained through repetition of complex experiments. However, generally, the deviation of the above-mentioned factors cannot be corrected using a single set value, so the switching of an output level in response to work and the automatic setting of output linked with a humidity sensor or the like are performed.
However, the switching of output level in response to work entails much labor and the difficulty of judging switching timing. Also, it is necessary to hold each of the plurality of the output levels from the charger in memory and the apparatus is expensive. Further, where output is automatically switched using a humidity sensor, an expensive humidity sensor is needed and the detected humidity sometimes does not correspond to the actual moisture content of a toner and a transfer material.
Generally, since the change in the atmospheric humidity acts on a toner and a transfer material with a certain time lag, accurate humidity detection is of no use. To use a humidity sensor effectively, a number of experiments and a complex, high-voltage control program are needed.